1. Technical Field
This invention relates to rope braking systems, more specifically to systems which brake the movement of a rope being used to lift or haul a load.
2. State of the Art
A rope braking system is used to brake the movement of a rope that has broken while being used to support or lift a weight. Braking the movement of a rope means stopping its movement, or halting payout of a rope so that any load carried by the rope does not fall. Ropes such as wire ropes can be used with a pulley. A rope and a pulley can be used to lift or haul a weight. A sheave is the wheel of a pulley having a grooved rim for holding the rope. A crane block includes a pulley and a hook for attaching a load. Modern cranes use crane blocks having multiple sheaves. The multiple sheaves allow the load to be spread over multiple loops of rope, allowing loads to be lifted that are heavier than a single strand of wire rope could lift. “Cable” is an archaic word for wire rope, which has been disfavored since communications cables have become well known.
U.S. Pat. No. 6,378,650 discloses a rope brake with a pivotable pulley that can be rotated to first or second sides against first or second side fixed wedges to compress the rope and thereby brake the rope. The braking can be released by rotating the pulley to the center.
U.S. Pat. No. 5,924,522 discloses a cable grab that uses a levered cam for a personal safety device application. U.S. Pat. No. 5,156,240 discloses a rope grab that also uses a levered cam for a personal safety device application.
U.S. Pat. No. 4,264,056 discloses a pulley with a rotatable sheave and a non-rotating sheave, where engaging the rope on the non-rotating sheave provides braking action.
U.S. Pat. No. 4,027,748 discloses a braking device for ropes that uses multiple bends of rope around pins for braking action.
U.S. Pat. No. 4,569,507 discloses a traction block for a linear winch that operates on a single strand of rope and seizes the rope by compressing halves of a clamping block in a tapered channel formed by flanges with rollers between the clamping block and the flanges.
Occasionally, a rope will break while in use, causing the load to descend out of control and leading to damage to the load, whatever the load lands on, and possibly death or serious injury to humans. When the rope is part of a crane system, the crane operator may react quickly enough to mitigate the damage, but a broken wire rope on a crane under load usually causes catastrophic damage, despite best effort.
There is, therefore a need for a method and apparatus for making safe a load, a crane head, a crane, and nearby personnel in response to a broken rope and to accomplish this with great speed.